Cubic membranes: a structure-based design for DNA uptake.

Cubic membranes are soft three-dimensional crystals found within cell organelles in a variety of living systems, despite the aphorism of Fedorov: 'crystallization is death'. They consist of multi-bilayer lipid-protein stacks, folded onto anticlastic surfaces that resemble triply periodic minimal surfaces, forming highly swollen crystalline sponges. Although cubic membranes have been observed in numerous cell types and under different pathophysiological conditions, knowledge about the formation and potential function(s) of non-lamellar, cubic structures in biological systems is scarce. We report that mitochondria with this cubic membrane organization isolated from starved amoeba Chaos carolinense interact sufficiently with short segments of phosphorothioate oligonucleotides (PS-ODNs) to give significant ODNs uptake. ODNs condensed within the convoluted channels of cubic membrane by an unknown passive targeting mechanism. Moreover, the interaction between ODNs and cubic membrane is sufficient to retard electrophoretic mobility of the ODN component in the gel matrix. These ODN-cubic membrane complexes are readily internalized within the cytoplasm of cultured mammalian cells. Transmission electron microscopic analysis confirms ODNs uptake by cubic membranes and internalization of ODN-cubic membrane complexes into the culture cells. Cubic membranes thus may offer a new, potentially benign medium for gene transfection.     

Charge transfer through DNA: A selective electrochemical DNA biosensor

The charge-transfer properties of DNA duplexes are exploited to produce a fast, simple, sensitive, and selective DNA biosensor by exposing the DNA recognition interface to a sample containing target DNA and the redox-active intercalator, anthraquinonemonosulfonic acid (AQMS). Electrochemistry from electron transfer through the DNA to AQMS intercalated into DNA duplexes can be differentiated from electrochemistry due to direct access of the AQMS to the electrode surface due to the difference in the environment of the AQMS giving a shift in the potential at which the molecule is reduced. The ability to distinguish between the two electrochemical signals enables DNA hybridization to be monitored in real time. This in situ detection scheme has good selectivity, being able to differentiate between a complementary target DNA sequence and one containing either C-A or G-A single-base mismatches. The concentration detection limit of the biosensor is 0.5 nM (1 pmol) with an assay time of 1 h. The fact that the end user is only required to simultaneously add the sample containing the target DNA and AQMS gives a DNA biosensor that is highly compatible with PCR on chip technologies.     

Inside Front Cover: Conjugated‐Polymer/DNA Interpolyelectrolyte Complexes for Accurate DNA Concentration Determination (Adv. Mater. 7/2006)

A water soluble cationic conjugated polymer that changes emission color from blue to green when going from dilute to concentrated conditions has been designed in work reported by Bazan and co‐workers on p. 878. Electrostatic complexation with anionic double‐ or single‐stranded DNA results in an increase of the local concentration of the conjugated polymer. The resulting changes in the emission spectra can be analyzed to provide an accurate determination of DNA concentration.     

Video analysis of DNA sequence homologies.

A method for the rapid quantitative analysis of dot blot assays is presented. A video camera, an NTSC compatible frame grabber board, and an AT personal computer are used to read photographic exposures of the assay plate. Image processing and image analysis techniques are used to calculate the orientation of the dot raster and then to compensate for the effect of variations in field illumination on measurements of local contrast. Local contrast (between dots and background) is an exponential function of the amount of hybridization between blotted DNA and complimentary oligonucleotide probes. The amount of hybridization between blotted DNA and oligonucleotide probes of known sequence is the criteria used to establish HLA-DR tissue types. Although the assay described here utilizes a chemiluminescent reaction, this algorithm may be used to read any assay that produces a rectangular raster of dots.     

结构DNA纳米技术:利用链霉亲和素-生物素相互作用增强DNA纳米结构的稳定性(英文)

实现纳米尺寸物体的合理设计与组装是纳米技术与精密工程的主要目标之一.DNA因其双链相互作用和螺旋几何构型的可预测性而使其成为构建纳米尺度结构的优秀建筑基元.DNA纳米结构在溶液状况改变时易分解.为提高DNA纳米结构的稳定性,一个链霉亲和素-生物素复合单元被引入到该纳米结构中.凝胶测试与熔点测试均证实链霉亲和素-生物素复合有助于提高DNA纳米结构的稳定性.该方法可广泛用于解决结构DNA纳米技术中的类似问题.     

DNA sequencing using capillary array electrophoresis.

A DNA sequencing method is presented that utilizes capillary array electrophoresis, two-color fluorescence detection, and a two-dye labeling protocol. Sanger DNA sequencing fragments are separated on an array of capillaries and detected on-column using a two-color, laser-excited, confocal-fluorescence scanner. The four sets of DNA sequencing fragments are separated in a single capillary and then distinguished by using a binary coding scheme where each fragment set is labeled with a characteristic ratio of two dye-labeled primers. Since only two dye-labeled primers are required, it is possible to select dyes that have identical mobility shifts. It is also shown that the ratio of the signal in the two detection channels provides a reliable identification of the sequencing fragment. DNA sequencing results on a 25-capillary array are presented.